The invention relates to a device for the continuous measurement of the liquid level in a container, particularly a fuel container of a motor vehicle, with a capacitive sensing element comprising a number of oblong electrodes embedded in an insulating material, which sensing element is the oscillation-determining element of an oscillator including one or more electric circuits in a structure that permits the generation of highly resistant input impedances, as dislosed, for example in copending application Ser. No. 841,111, filed Oct. 11, 1977 to Jung et al, now U.S. Pat. No. 4,142,415 issued Mar. 6, 1979 and German application P 27 47 326.
A device of this kind is, as stated in the copending aplications noted above, particularly suitable for measuring the level of liquid with a small relative dielectric constant, such as gasoline, since the device of the invention has sufficient sensitivity to measure and utilize the capacity change between a full and empty container or tank.
A special advantage of the sensing element of the invention is that almost any desired calibration characteristic can be produced so that the device can be used even in containers of complicated shape, and an accurate indication of the residual quantity can be obtained. The setting of the desired calibration characteristic is particularly simple when a flexible, band-shaped sensing element is employed, and adjustment or manufacture of the sensing element in the desired form are required. Another possible construction is a sensing element with rigid electrodes whose width varies along their longitudinal axes. In the latter sensing device, additional means for calibration of the sensing element are unnecessary, but the production of the calibration characteristic is more expensive than in the case of the sensing element first mentioned above.
A further type of prior art device is disclosed in British patent No. 819,712 of 1959.